Trialkylene diamine initiators for the polymerization of formaldehyde



Patented July 2, 1963 of Delaware No Drawing. Filed Feb. 13, 1961, Ser. No. 88,628 7 Claims. (Cl. 260-67) This invention relates to a process for the preparation of tough, high molecular weight polymers of formaldehyde. More particularly it relates to the use of trialkylene diamines as polymerization initiators in the preparation of these formaldehyde polymers.

It is known that formaldehyde can be polymerized in the presence of such polymerization initiators as metal salts, phosphines, arsines, stilbenes, and certain mono amines to form tough, high molecular weight polyoxymethylene which can be used in the preparation of films, fibers, filaments, and molding compositions. It has now been found that another class of compounds can be used in the preparation of these formaldehyde polymers.

In accordance with the present invention, substantially anhydrous monomeric formaldehyde is contacted with the novel polymerization initiator and allowed to polymerize to high molecular weight polyoxymethylene.

The novel polymerization initiators that are employed in this process are tertiary diamines which have the formula /Alkylene\ N-A lkyleneN Alkylcno The alkylene groups are saturated, straight-chain or branched chain aliphatic hydrocarbon groups which contain from 2 to 4 carbon atoms. Among the specific compounds that may be used are triethylene diamine, tripropylene diamine, triisopropylene diamine, and tributylene diamine. A single trialkylene diamine or a mixture of two or more of these compounds may be used.

The amount of the initiator that is used is generally between about 0.00001 part and 0.05 part and preferably between about 0.0001 part and about 0.005 part by weight per part by weight of formaldehyde.

The polymerization reaction may be carried out in the presence or in the absence of a liquid reaction medium or in a vapor phase reaction. it is preferably carried out in a substantially anhydrous organic medium which remains liquid under the conditions chosen for the reaction, which is inert to formaldehyde and to the polymerization initiator, and which is a nonsolvent for polyoxymethylene. Suitable reaction media include hydrocarbons, chlorinated hydrocarbons, ethers, and the like. The preferred media are the hydrocarbons which contain from 3 to carbon atoms, such as propane, hexane, octane, decane, cyclohexane, benzene, xylene, and decahydronaphthalene.

The amount of the reaction medium used is not critical but may be within the range of about 1 to 1000 parts by weight per part by weight of formaldehyde. In most cases about 1 to 150 parts of the medium is used for each part of formaldehyde.

The polymerization may be carried out in any convenient manner. For example, anhydrous monomeric formaldehyde may be introduced into a reactor containing a reaction medium and the polymerization initiator. Alternatively, the polymerization may be carried out by introducing formaldehyde continuously into a reactor containing the reaction medium and at the same time adding the polymerization initiator at such a rate that the temperature is maintained within the range chosen for the polymerization.

The conditions under which the formaldehyde is po lymerized are not critical. The polymerization is generally effected at a temperature between about C. and 80 C. and preferably between 0 C. and 40 C. While superatmospheric and subatmospheric pressures may be employed, the reaction in most cases takes place under atmospheric pressure.

The formaldehyde monomer that is used as the starting material in this process may be derived from any convenient source. For example, it may be obtained by pyrolysis of paraformaldehyde, a-polyoxymethylene, or a hemiformal such as cyclohexanol hemiformal. In order to obtain the desired tough, high molecular weight product, it is necessary that the formaldehyde monomer be substantially anhydrous, that is, that it contain less than 0.5% and preferably less than 0.1% by weight of water.

The formation of tough, high molecular weight polyoxymethylene is best effected under non-oxidizing conditions. A convenient way of obtaining such conditions involves sweeping the reactor with a dry inert gas, such as nitrogen, and then carrying out the reaction under a blanket of the inert gas. In addition an antioxidant may be present during the reaction or may be added to the product to reduce oxidative effects. Among the, antioxidants that may be used for this purpose are phenothiazine, Z-mercaptobenzimidazole, diphenylamine, phenyl-ot-naphthylamine, bis (@naphthylamino -p-phenylenediamine, and S-ethyl-IO,lO-diphenylphenazasiline. The amount of antioxidant used is generally about 0.01% to about 1% based on the weight of the formaldehyde.

The manner in which this invention may be practiced is illustrated by the following example. It is to be understood, however, that this example is not to be construed as being limitative but is furnished merely for purposes of illustration.

Example Five hundred and twenty grams of cyclohexanol hemiformal which contained 23.3% of formaldehyde was heated at 108148 C. over a period of approximately 2 hours. The formaldehyde vapors from the pyrolysis were passed through a series of traps, the first of which was maintained at 55-95 C., the second at 0 C., and the third and fourth at 4 to -20 C. The anhydrous monomeric formaldehyde that was produced was introduced along with a stream of dry nitrogen into a reactor which contained 1000 ml. of cyclohexane, 0.1 gram of phenothiazine, and 0.078 gram of triethylene diamine. The reaction mixture was stirred vigorously during the addition of the formaldehyde. The polymerization Was carried out at room temperature in a nitrogen atmosphere. When the polymerization was complete, the reaction mixture was filtered. The product was washed with 300 ml. of cyclohexane and dried under vacuum at 70 C. to constant weight. The product, which weighed 41.2 grams, may be molded, for example, at C. for 2 minutes to form tough molded objects.

Each of the other trialkylene diamines that have been disclosed herein may be employed in a similar manner in initiate the polymerization of formaldehyde to form tough, high molecular weight polyoxymethylene.

Formaldehyde polymers prepared in accordance with this invention may be converted by melt extrusion, in jection molding, compression molding, and other fabrication methods to films, fibers, molded articles, and the like.

What I claim is:

I. A process for the production of high molecular weight polyoxymethylene which comprises contacting substantially anhydrous monomeric formaldehyde at a temperature in the range of approximately 100 C. to 80 C. with a polymerization initiator which is a trialkylene diamine having the formula /Alkylcne Alkylene wherein the alkylene groups are saturated aliphatic hydrocarbon groups which contain from 2 to 4 carbon atoms, said polymerization initiator being present in the amount of approximately 0.00001 part to 0.05 part by weight per part by Weight of said formaldehyde.

2. The process of claim 1 wherein the polymerization initiator is trethylene diarnine.

3. The process for the production of high molecular weight polyoxymethylene which comprises introducing substantially anhydrous monomeric formaldehyde into a reaction medium maintained at 100 C. to 80 C., said medium comprising a liquid hydrocarbon containing 3 to carbon atoms per molecule and a polymerization initiator, said polymerization initiator being a trialkylene diamine having the formula Alkylono N.t\ llrylene-N .Alkylene wherein the alkylene groups are saturated aliphatic hydrocarbon groups which contain from 2 to 4 carbon atoms, and being present in the amount of approximately 0.00001 part to 0.05 part by weight per part by weight of said formaldehyde and recovering high molecular weight polyoxymethylene.

4. The process for the production of high molecular weight polyoxymethylene which comprises introducing substantially anhydrous monomeric formaldehyde into a reaction medium maintained at 0 to C., said re action medium comprising a liquid hydrocarbon con.- taining 3 to 10 carbon atoms per molecule, an antioxidant, and a polymerization initiator, said polymerization initiator being a trialkylene diamine having the formula Alk ylene N-Alkylune-N A lkylene wherein the alkylene groups are saturated aliphatic hydrocarbon groups which contain from 2 to 4 carbon atoms, and being present in the amount of approximately 0.00001 part to 0.05 pant by weight per part by weight of said formaldehyde, agitating said reaction medium and forming a dispersion of high molecular weight polyoxymethylene in said medium, and thereafter recovering the polyoxymethylene.

5. The process of claim 4 wherein the polymerization initiator is present in the amount of about 0.0001 part to about 0.005 part by weight per part by weight of formaldehyde.

6. The process of claim 5 wherein the reaction medium is present in the amount of 1 part to parts by weight per part by weight of formaldehyde.

7. The process of claim 6 wherein the polymerization initiator is triethylene diamine.

References Cited in the file of this patent UNITED STATES PATENTS 2,841,570 MacDonald July 1, 1958 

1. A PROCESS FOR THE PRODUCTION OF HIGH MOLECULAR WEIGHT POLYOXYMETHYLENE WHICH COMPRISES CONTACTING SUBSTANTIALLY ANHYDROUS MONOMERIC FORMALDEHYDE AT A TEMPERATURE IN THE RANGE OF APPROXIMATELY -100*C. TO 80*C. WITH A POLYMERIZATION INITIATOR WHICH IS A TRIALKYLENE DIAMINE HAVING THE FORMULA 